Demonstration of optical frequency comb generation using four-wave mixing in highly nonlinear fiber

Abstract

We demonstrate a broad and flat optical frequency comb (OFC) by exploiting the four-wave mixing experienced by optical signals propagating through the highly nonlinear fiber. We modulate two 50 GHz spaced continuous wave laser signals using single mach-zehnder modulator controlled by 25 GHz periodic radiofrequency signal which results in a broad but non flat and non-coherent OFC. 400 m long highly nonlinear fiber (HNLF) is used to initialize the four wave mixing and induce the coherency between the OFC frequency lines. The flatness and broadness of optical frequency comb further enhanced by passing it through a 500 m long fiber. By managing a highly nonlinear fiber length compared to the coherence length, nonlinear coefficient, and injected optical power inside two-stage cascaded erbium-doped fiber amplifier (EDFA) and HNLF, an optical frequency comb of 55 frequency lines with 3 dB maximum power deviation is realized.